A top Syrian rebel leader said his forces were drawing new recruits away from extremist groups like Jabhat al Nusra.

PARIS—A top Syrian rebel leader said his forces were counting on arms shipments from the U.S. to reverse momentum in the country's civil war and draw new recruits away from extremist groups like Jabhat al Nusra.

In an interview with The Wall Street Journal, Brig. Gen. Mithkal Albtaish—a leader of the Free Syrian Army, or FSA—said he has recently persuaded 60 fighters to shift allegiance from al Nusra, a radical Islamist group aligned...